BASIC KEYSTONE PRODUCT INSTALLATION
The Keystone Retaining Wall System was developed with simplicity of construction in mind. These step-by-step instructions will guide you
through the basic process from start to finish. If more detailed information is required to meet your specific site situation, consult your local
Keystone representative.
Step 1. Prepare the Base Leveling Pad.
Remove all surface vegetation and debris. Do not use this material as backfill. After selecting the location
and length of the wall, excavate the base trench to the designed width and depth. Start the leveling pad at
the lowest elevation of the wall. Level the prepared based with 6" of well-compacted granular fill (gravel,
road base, or ½" to ¾" [13 - 20 mm] crushed stone). Compact to 95% Standard Proctor or greater.
Keystone recommends additional trench depth for below grade placement of Keystone units on a ratio of
1" (25 mm) below grade for each 8" (200 mm) of wall height above grade (to a maximum of 3 units
buried). This lowers the base course below grade locking the wall in place and also helps prevent erosion
and scouring at the base of the wall. The base trench should be wide enough to allow for the Keystone unit
and drainage zone. An option to a compacted, granular material leveling pad is to use a non-reinforced
concrete leveling pad. In some cases, contractors find this is a time-saving approach. Walls built to a level
condition on a sloping grade require a stepped based. It is best to work out the stepped base as the wall steps up in elevation. If a concrete
leveling pad is used, the step-up height needs to exactly match the Keystone unit height.
Step 2. Install the Base Course.
Place the first course of Keystone units side by side (with sides touching) on the prepared base, with the
paired pin holes facing up. Make sure each unit is level - side to side and front to back. The first course is
critical for accurate and acceptable results. For alignment of straight walls, use the pins or the straight
back edge of the unit. Using the front face will give irregular alignment due to the rough split texture.
Step 3. Insert the Interlocking Fiberglass Pins.
Place the reinforced fiberglass pins into the paired holes (2) of each
keystone unit. (Pins of adjoining units should be 12" [305 mm] on
center.) Once paced, the pins create an automatic setback for the
additional courses. According to wall requirements and design, place
pins in the front holes for near vertical (1/8" or [3 mm]) setback and
the rear holes for 1¼" (32 mm) setback per course. for constructing
curved walls, use the front pin position for best results. Minimum
radius for convex and concave curves is 3'6" (1 m).
Step 4. Install and Compact Backfill.
Fill in all voids - in and between Keystone units - using ½" to ¾" (13 - 20 mm) clean crushed stone. Place
drain zone behind the units as required to achieve total 2 ft. (0.6 m) depth of drainage zone from unit face.
Peagravel should not be used. Compact material in unit cavities appropriately to eliminate settling.
Next, if economical, use existing soils for backfill behind the drainage zone. (Heavy clays or organic soils
are not recommended due to water-holding properties.) In some situations poor site soils will cause
higher reinforcement costs, so economics of using import soils should be reviewed. Compact soils to a
minimum of 95% Standard Proctor compaction, placing fill in 8" (200 mm) lifts on a course-by-course
basis or as specified by a Professional Engineer. (Use only walk-behind mechanical compaction
equipment within 3' [1 m] behind the units to avoid localized overstress). Sweep off any pebbles or debris
so the next Keystone units rest evenly upon the layer below.
